package year2021.month0234;

import java.text.MessageFormat;

public class MainTest {

    public static void main(String[] args){
        String str = MessageFormat.format("123{0}789", "456");
        System.out.println(str);
    }

}

class B{
    public B(int a){

    }
}
class A extends B{
    public A(){
        this("");
    }

    public A(String str){
        super(1);
    }
}